UOP 964-2011 Surface Area Pore Volume Average Pore Diameter and Pore Size Distribution of Porous Materials by Nitrogen Adsorption.pdf

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1、 IT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TO DETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH AND SAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THIS PROCEDURE IN THE MANNER PRESCRIB

2、ED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS (MSDS) OR EXPERIMENTAL MATERIAL SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED IN THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTION EQUIPMENT (PPE). COPYRIGHT 1998, 2011 UOP LLC. All rights reserve

3、d. Nonconfidential UOP Methods are available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, USA. The UOP Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service at serviceastm.org, 610.832.9555 FAX, or 610.83

4、2.9585 PHONE. Surface Area, Pore Volume, Average Pore Diameter, and Pore Size Distribution of Porous Materials by Nitrogen Adsorption UOP Method 964-11 Scope This method is for determining the surface area (SA), total pore volume (PV), average pore diameter (PD), and pore size distribution from 2 to

5、 approximately 60 nm (20 to 600 angstroms) of porous materials. The method describes the standard procedure for analysis, data collection and reporting using a commercially available instrument. References E. Barrett, L. Joyner and P. Halenda, J. Amer. Chem. Soc., 73, 373 (1951) S. Brunauer, P. Emme

6、tt, and E. Teller, J. Amer. Chem. Soc., 60, 309 (1938) I. Langmuir, J. Amer. Chem. Soc., 40, 1361 (1918) UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Outline of Method The sample is degassed using heat and vacuum. After weighing, it is cooled in liquid nitrogen. The amount of

7、nitrogen gas adsorbed on the sample is measured at various predetermined pressures. The instrument computer processes the data and calculates surface area, total pore volume, average pore diameter, and pore size distribution based on the isotherm. The results are printed and/or plotted as desired (s

8、ee Report). Definitions BET surface area, estimated surface area for non-porous materials using the equation derived by Brunauer, Emmett, and Teller, surface area calculated at P/P0 = 0.10, 0.15, 0.20, 0.25, 0.30 BET surface area can be calculated at P/P0 points other than the standard above. P/P0 =

9、 0.03 and 0.3 are common for certain materials (See Appendix B). Langmuir surface area, estimated surface area for microporous materials using the equation derived by Langmuir, surface area calculated at P/P0 = 0.10, 0.15, 0.20, 0.25, 0.30 2 of 6 964-11 P, endpoint pressure for a specific data point

10、 P0, vapor pressure of the adsorbate gas P/P0, relative pressure of the adsorbate t-Plot, plot of statistical thickness of the adsorbed layer of gas versus the adsorbed volume of the adsorbate gas Apparatus References to suppliers and catalog numbers are included as a convenience to the method user.

11、 Other suppliers may be used. Balance, analytical, readable to 0.0001 g Crucible, high form, 5-mL, porcelain, Fisher Scientific, Cat. No. 07-965B, with cover, Fisher Scientific, Cat. No. 07-970C, optional, see Procedure, Sample Pretreatment, Step 3, bullet Desiccator, 160-mm ID, and porcelain plate,

12、 Fisher Scientific, Cat. Nos. 08-632 and 08-641A, respectively, optional, see Procedure, Sample Pretreatment, Step 3, bullet Dewar, liquid nitrogen Gloves, heat resistant, Zetex, VWR, Cat. No. 32885-407 Gloves, cryogenic, VWR, Cat. No. 32885-757 (for size large) Muffle furnace, capable of at least 5

13、00C Regulator, helium, two-stage, high purity, delivery pressure range 15 -200 kPa (2-30 psi), Matheson Tri-Gas, Model 3121-580 Regulator, nitrogen, two-stage, high purity, delivery pressure range 15 -200 kPa (2-30 psi), Matheson Tri-Gas, Model 3121-580 Sorption analyzer, automatic, any commercially

14、 available computer controlled system is adequate, with the following accessories. Micromeritics and Quantachrome are two suppliers of this equipment. Caps or stoppers, sized to fit sample cells (will differ depending on manufacturer) Sample cells, pellet and powder Stem inserts, void volume reducer

15、s (optional) Timer, 10 minute to 2 hour Tongs, stainless steel, crucible, Fisher Scientific, Cat. No. 15-186, optional, see Procedure, Sample Pretreatment, Step 3, bullet Vacuum oven, laboratory, capable of 150C, with pump Reagents and Materials References to suppliers and catalog numbers are includ

16、ed as a convenience to the method user. Other suppliers may be used. Glass wool, VWR, Cat. No. EM-GX0090-2. Glass wool is not needed for most samples, but may be used to retain powder samples when vacuum is applied. 3 of 6 964-11 Desiccant, indicating Drierite, 8-mesh, Fisher Scientific, Cat. No. 07

17、-578-3A, optional, see Procedure, Sample Pretreatment, Step 3, bullet Helium gas, 99.995% minimum purity Nitrogen gas, 99.997% minimum purity Nitrogen, liquefied Procedure Install and initialize the instrument following the manufacturers directions. The instructions in the manual are essential for c

18、orrect operation of the instrument and should be fully understood before any attempt is made to analyze samples. Sample weight can be determined prior to analysis by using a tared sample cell or following analysis using the measured cell weight. The procedure in Appendix A describes the steps to mea

19、sure the tared cell weight. Sample Pretreatment 1. Weigh approximately 0.250 g, to the nearest 0.0001 g, of a representative sample into a clean, dry, sample cell (tared cell if known). Note: The amount of sample needed for analysis will vary with the expected Surface Area. A 0.250 g sample is suffi

20、cient for a material with a Surface Area between 100 and 750 m2/g. 2. For samples known to be clean, proceed to Step 3. Use the following procedure to degas large amounts of moisture or light hydrocarbons from the sample. Place the sample on the degas rack and set the initial temperature to 90C. Eva

21、cuate for 60 1 minutes. Increase the temperature to 150C and hold until the vacuum returns to 0.07 kPa or less. Raise the temperature to the final preparation temperature and proceed. Alternatively, a contaminated sample can be placed in a 150C vacuum oven for 2 to 4 hours prior to transferring to t

22、he instrument. 3. Place the sample on the degas rack and set the heating mantle to 300oC (typically for BET) or 400oC (typically for samples with extensive micropore structure), depending on the instrument and the nature of the sample; some polymer samples may only be able to be heated to 100C. Load

23、 the sample following the manufacturers instructions and degas for 2 to 16 hours, depending on the degree of micropore structure expected in the sample (fresh alumina catalysts require less time to degas, 2 hours is generally sufficient; while samples containing extensive micropore structure, such a

24、s zeolites, require up to 16 hours). If the sample needs to be treated at 400C, and the instrument is not capable of achieving 400C, place the sample in a 400C muffle furnace for 2 to 4 hours prior to degassing. Cool in a desiccator. 4. Perform a leak check on each sample at temperature by isolating

25、 the sample and monitoring for any pressure change for 10 minutes. The pressure in the sample cell should not change by more than 0.0001 kPa. If the pressure change exceeds 0.0001 kPa, apply heat and vacuum and recheck after 2 hours. If the pressure still changes, bring the sample to atmospheric pre

26、ssure with helium, and re-seat the seal. Apply heat and vacuum again and recheck after 2 hours. 5. Turn off the heating mantle and allow the sample to cool to room temperature. 6. Remove the sample cell from the instrument following the manufacturers instructions and cap. If a tared cell is used wei

27、gh the sample cell to the nearest 0.0001 g. Subtract the tare mass to obtain the degassed sample mass. 7. Repeat Steps 1 through 5 for any additional samples. 4 of 6 964-11 Sample Analysis 1. Fill the dewar with liquid nitrogen to the proper level. CAUTION: Use appropriate personal protective equipm

28、ent when working with cryogenic liquids such as liquid nitrogen. Consult the MSDS and local regulations for guidance. 2. Place the sample cell on an analysis port and input the sample identification data following the manufacturers instructions. Select the appropriate analysis sequence and report fo

29、rmat for the sample. Table 1 contains the relative pressure points and calculation assignments for a typical 20-point adsorption isotherm. The pressure points can be adjusted depending on resolution and material type if needed. 3. Initiate the run sequence to automatically analyze the sample. 4. Rep

30、eat Steps 1 through 3 for any additional samples that have completed the pretreatment procedure, using the remaining analysis ports. Table 1 Measurement Points for a Typical Adsorption Isotherm P/P0 Description P/P0 Description 0.05 A P 0.55 A P 0.10 AM P 0.60 A P 0.15 AM P 0.65 A P 0.20 AM P 0.70 A

31、 P 0.25 AM P 0.75 A P 0.30 AM P 0.80 A P 0.35 A P 0.85 A P 0.40 A P 0.90 A P 0.45 A P 0.95 A P 0.50 A P 0.967 A VP where: A = Adsorption point M = Multi-point BET/Langmuir Surface Area point V = total pore Volume point P = Pore size distribution point Calculations All surface area, pore volume, and

32、t-plot calculations are performed by the instrument software and the results are displayed on the monitor for review. The results can subsequently be reprocessed and printed as desired. Surface area, total pore volume, and pore size distribution are calculated using user selected data reduction para

33、meters. Summaries of the theory are given in the instrument manual. Report Data reports are configured as desired. The report can contain any or all of the following: the isotherm (multi-point), pore diameter and/or volume distribution (multi-point), and/or the calculated surface area (multi-point o

34、r single-point). Examples of report formats and setup procedures are described in the instrument operating manual. Report surface area to the nearest m2/g, not to exceed 3 significant figures 5 of 6 964-11 Since surface area analysis of the same material can yield different values depending on sampl

35、e measurement parameters and pretreatment conditions, surface area data must be reported with a description of how it was obtained, the preparation conditions and the pressure points used, so that if the work is to be duplicated, the same pressure table can be used. This should ensure that data comp

36、arisons are made only on data obtained in the same manner. This descriptive data should be listed on all reports to customers to ensure that data comparisons are only done on data collected in like manner, even if the data are collected at different times in different locations. Precision Precision

37、statements were determined using UOP Method 999, “Precision Statements in UOP Methods.” Repeatability, Site Precision, and Reproducibility A nested design was carried out for determining BET and Langmuir surface area and pore volume for two catalyst samples with three laboratories and two analysts i

38、n each laboratory. Each analyst carried out tests on two separate days, performing two tests on each sample each day. The total number of tests was 48. The precision data are summarized in Table 2. Two tests performed by the same analyst on the same day should not differ by more than the repeatabili

39、ty allowable difference with 95% confidence. Two tests performed in one laboratory by different analysts on different days should not differ by more than the site precision allowable difference with 95% confidence. Two tests performed in different laboratories should not differ by more than the repr

40、oducibility allowable difference with 95% confidence. Table 2 Repeatability, Site Precision, and Reproducibility Repeatability Site Precision Reproducibility Sample/ Analysis Mean Within- Day esd Allowable Difference Within- Lab esd Allowable Difference Between-Lab esd Allowable Difference Sample 1/

41、 BET Surface Area, m2/g 212 3.3 11 3.5 13 4.0 13 Sample 2/ Langmuir Surface Area, m2/g 676 7.6 30 9.8 37 16.7 58 Sample 2/ Pore Volume, mL/g 0.39 0.008 0.03 0.010 0.04 0.030 0.10 Time for Analysis The elapsed time for analysis varies with the degree of porosity of the sample. Typical elapsed times f

42、or catalyst samples are in the range of 12 to 30 hours. The labor requirement is one hour per sample. Suggested Suppliers Fisher Scientific, 711 Forbes Ave., Pittsburgh, PA 15219-4785, USA (412-490-8300) Matheson Tri-Gas, 166 Keystone Dr., Montgomeryville, PA 18936, USA (215-641-2700) 6 of 6 964-1

43、1 Micromeritics Instrument Corporation, One Micromeritics Dr., Norcross, GA 30093-1877, USA (770-662-3620) Quantachrome Instruments, 1900 Corporate Dr., Boynton Beach, FL 33426, USA (561-731-4999) VWR International, 1310 Goshen Pkwy., West Chester, PA 19380, USA (610-431-1700) Appendix A Sample C

44、ell Tare Mass Determination 1. Attach clean, dry, empty cells to the degas positions of the instrument following the manufacturers instructions. 2. Evacuate the empty cells for 5 1 minutes. Do not heat the cells during this step. 3. Unload the cells following the manufacturers instructions. When the

45、 instrument has completed the operation and the cells are backfilled with helium, remove the cells and cap immediately. 4. Weigh the cells to the nearest 0.0001 g. Record the mass of the helium filled cell and cap (and stem insert if used). This is the sample cell tare mass. Appendix B BET Surface A

46、rea Calculated at 0.03 P/P0 The single point BET surface area at 0.03 P/P0 is calculated to three significant figures using the equation below. The unit cc (cubic centimeter) is interchangeable with mL (milliliter). Depending on the instrument being used, either may be printed out on reports, althou

47、gh cc appears to be the convention. A = 4.22 Vads (B1) where: A = BET surface area at 0.03 P/P0, m2/g Vads = volume adsorbed at 0.03 P/P0, cc/g 4.22 = the constant 4.35 adjusted for the slope at 0.03 P/P0 4.35(P0-P)/P0, m2/cc BET Surface Area Calculated at 0. 3 P/P0 The single point BET surface area

48、 at 0.3 P/P0 is calculated to three significant figures using the equation below. The unit cc (cubic centimeter) is interchangeable with mL (milliliter). Depending on the instrument being used, either may be printed out on reports, although cc appears to be the convention. A = 3.04 Vads (B2) where: A = BET surface area at 0.3 P/P0, m2/g Vads = volume adsorbed at 0.3 P/P0, cc/g 3.04 = the constant 4.35 adjusted for the slope at 0.3 P/P0 4.35(P0-P)/P0, m2/cc